The present invention relates to a hydraulic brake system for automotive vehicles comprising a brake master cylinder connected to an unpressurized reservoir. A brake line communicates with a working chamber of the brake master cylinder and leads to pressure control valves of a brake slip control apparatus. Connected downstream of the valves is at least one wheel brake.
In brake systems of this type, a quantity of pressure fluid is required during operation of the brake slip control apparatus for the repeated actuation of the wheel brake after a pressure discharge. The required quantity significantly exceeds the delivery rate of the brake master cylinder. Therefore, the operation of the brake slip control apparatus necessitates that the wheel brake is supplied with pressure fluid out of an additional pressure-fluid source, for example, an energy supply system, independently of the brake master cylinder.
A brake system is known from patent application P 34 39 258.0, wherein there is provision of a brake power booster fed by a hydraulic energy supply system for the actuation of the brake master cylinder. The brake line in this brake system is connectable with the booster chamber of the brake power booster by way of an electromagnetically actuatable control valve of the brake slip control apparatus and by way of a non-return valve connected downstream thereof. This supplies the wheel brake cylinders with pressure fluid out of the energy supply system of the brake power booster during operation of the brake slip control apparatus. Further more, a controllable non-return valve is interposed between the brake master cylinder and the connecting point of the control valve, which non-return valve is caused by the pressure metered through the control valve to assume a closed position in which only return flow of pressure fluid to the brake master cylinder is kept in a standby position during operation of the brake slip control apparatus. However, this solution is restricted to brake systems which comprise a hydraulic brake power booster. Such brake systems entail comparatively high costs and, therefore, are not commercially acceptable for smaller vehicles. Another shortcoming of this brake system is that the proper functioning of the hydraulic brake power booster and that of the brake slip control apparatus are dependent on one another.
Therefore, it is the object of the present invention to devise a brake system of the type initially referred to which, while requiring little structural and monitoring efforts, affords an energy supply for the brake slip control apparatus which is independent of the actuating system of the brake master cylinder.